1. Field of the Invention
The present invention relates to a printer, and more specifically, to a printer which is capable of controlling a data printing period.
2. Description of the Prior Art
With the rapid development of printing equipment, printers have become necessary peripheral devices. Inkjet printers, due to their cheap prices and excellent print quality, have become one of the most popular printing apparatuses.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a block diagram of an inkjet printer 10 according to the prior art. FIG. 2 shows a waveform of a phase signal produced by a phase encoder 11 shown in FIG. 1. The inkjet printer 10 comprises the phase encoder 11, a print signal generator 12, a data transducer 14, a head driver 16 and a printhead 18. The phase encoder 11 produces phase signals A and B for recording the position of the printhead 18 as the printhead 18 moves. The print signal generator 12 produces a print signal as the printhead 18 moves at a constant speed to a predetermined position. As can be seen in FIG. 2, the print signal generator 12 will generate a print signal whenever the printhead 18 moves to the position N, N+1, N+2, etc. (as the phase signal A or B changes), where the distance between N, N+1, N+2, etc. is fixed. After receiving a printing signal, the data transducer 14 will download the raw data, and ultimately, the head driver 16 will drive the printhead 18 to print the downloaded data.
Please refer to FIG. 3. FIG. 3 is a stable signal diagram, where the horizontal axis represents time, showing that the printed resolution at which the printer 10 prints is higher than the normal mode. Supposing that the normal mode of the printer 10 is 600 dpi (dots per inch), if the printer 10 works under the resolution of 600 dpi, the print signal generator 12 produces a print signal P1 as the printer 18 reaches the position N, produces a print signal P5 as the printer 18 reaches the position N+1, produces a print signal P9 as the printer 18 reaches the position N+2, and so on. If the printer 10 is operated in high resolution mode, the print signal generator 12 will determine a predetermined inkjet distance based on the selected high resolution and generate a print signal at the predetermined inkjet distance. For instance, when the printer 10 for which the normal mode is 600 dpi works at the high resolution of 2400 dpi, the printer 10 controls the printhead 18 to eject three ink drops between an interval of every two drops originally printed in normal mode by using interpolation. In other words, the print signal generator 12 will divide the time in which the printhead 18 previously took to move from the position N−1 to the position N into three equal ejecting times based on the desired resolution, and produces a print signal P2, P3, P4 at a constant rate. After receiving the print signal, the data transducer 14 will download the corresponding data in turns, and the head driver 16 will drive the printhead 18 to print the downloaded data. In this way, the printed resolution increases as the ejecting time in the unit length increases.
In order to eject additional ink drops with adequate time, however, the printhead 18 needs to slow down in the process of printing at the high resolution.
Please refer to FIG. 4 in conjunction with FIG. 3. FIG. 4 is an actual signal diagram showing that the printed resolution at which the printer 10 prints is higher than the normal mode. Even though the print signal generator 12 is capable of generating a print signal at each predetermined time according to the predetermined resolution, as previously mentioned, the printhead 18 must slow down in the process of printing at the high resolution. Nevertheless, the moves of the printhead 18 will be unstable at low speed due to mechanism used to move the printhead. As a result, even though the time which the print signal generator 12 generates a print signal is fixed, due to the unstable moving speed of the printhead 18, ejecting ink drops may possibly fall on the incorrect predetermined positions. As shown in FIG. 4, when Data8 has not yet been completely printed by the printhead 18, and the next print signal P9 is received by the transducer 14 and the raw data Data9 is downloaded, at this moment, the printhead 18 is printing the previous data Data8 with unstable velocity. Consequently, the print data generator 12 will ignore the print signal P9, and not inform the data transducer 14 to download the corresponding data Data9. When an upcoming print signal P10 is generated, the data transducer 14 will download the raw data Data9 instead, and the data transducer 14 will download the raw data Data10 as the print signal P11 is generated. Despite the total printed distance for each swath being predetermined, as well as the required times of the print signal for each swath, it is possible that after all required print signals for each swath are generated, some of the data still has not been downloaded and printed, causing a print error. As a result, downloading and printing the data corresponding to the print signals successfully is a problem desired to be solved.